No, but functions for their games get discontinued as the hardware they are from becomes limited. The days for the online functions of the 3DS are now numbered (faster than other nintendo hardware too since Nintendo wants to get every one paying for online as soon as possible)
Further, them being left behind means they can't reap any benefits from the newer generations. Imagine if you couldn't have every pokemon in X and Y and now you couldn't play with your favorite pokemon in Pokemon Amie?
Or what if one of your favorites just needed some better moves to make it a little more viable? Well it would be a shame if it couldn't get to gen 6 when play rough got added to so many old pokemon move sets, or gen 7 when Leech Life got a HUGE buff.
Not to mention all the quality of life improvements each games adds for breeding, training and shiny hunting. If your favorite pokemon isn;t in the latest game, you can never take advantage of those new improvements for that particular species.
If the decision doesn't bother you, that's fine, and I'm happy for you, but you can't act like there is no reason for people to be bothered by this just because you aren't.
Did you even read the part where I mentioned people with Pokemon that get cut do have a right to be annoyed? My point is there's simply a far greater portion of players (first-timers and those who don't care about transferring) that aren't severely impacted, if at all, from not having the full National Pokedex (and even fewer probably care about all the mechanics you mentioned, plus if you actually do have a substantial collection of trained Pokemon to transfer, isn't it already too late for them to benefit from breeding and training QOL?). Raising a huge stink is premature, especially when we don't know the full extent of Game Freak's plans, and also because this may be the norm going forward. Since the alternatives are:
a) Keep carrying on as they did before, advancing all aspects including roster, until development cycles become unmanageable,
b) Forgo any and all graphical (and possibly gameplay) advancements in favour of preserving and augmenting the roster. Fan games and sites have a monopoly on this however.
c) Stop making new Pokemon altogether and focus exclusively on balancing and features. Will almost assuredly lead to a slow death as new Pokemon are the primary selling point for the masses.
I do hope Game Freak has a plan to incorporate any Pokemon not in Sword & Shield at launch in the near future, even if it involves a separate set of games entirely, but the truth is concessions have to be made in order to make real progress elsewhere. Take a look at this latest video from Jwittz and you can see all things other JRPGs have done that Pokemon's missed out on as a result of focusing more on maintaining it's roster of Pokemon:
There's still a lot we don't know about the newest games, such as it's story or any potential villains.